Question: Ishaan is 24 years younger than Christopher. Christopher and Ishaan first met 3 years ago. Twelve years ago, Christopher was 4 times older than Ishaan. How old is Christopher now?
Solution: We can use the given information to write down two equations that describe the ages of Christopher and Ishaan. Let Christopher's current age be $c$ and Ishaan's current age be $i$ The information in the first sentence can be expressed in the following equation: $c = i + 24$ Twelve years ago, Christopher was $c - 12$ years old, and Ishaan was $i - 12$ years old. The information in the second sentence can be expressed in the following equation: $c - 12 = 4(i - 12)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $c$ , it might be easiest to solve our first equation for $i$ and substitute it into our second equation. Solving our first equation for $i$ , we get: $i = c - 24$ . Substituting this into our second equation, we get the equation: $c - 12 = 4($ $(c - 24)$ $ -$ $ 12)$ which combines the information about $c$ from both of our original equations. Simplifying the right side of this equation, we get: $c - 12 = 4c - 144$ Solving for $c$ , we get: $3 c = 132$ $c = 44$.